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J den Hertog

Publications and source records attributed to J den Hertog.

At least 19 recordsLinked to original sources
PubMed1999

Restoration of potent protein-tyrosine phosphatase activity into the membrane-distal domain of receptor protein-tyrosine phosphatase alpha.

Most transmembrane, receptor-like protein-tyrosine phosphatases (RPTPs) contain two cytoplasmic catalytic protein-tyrosine phosphatase (PTP) domains, of which the membrane-proximal domain, D1, contains the majority of the activity, while the membrane-distal domain, D2, exhibits little or no activity. We have investigated the structural basis for reduced activity in RPTP-D2s, using RPTPalpha as a model system. Sequence alignment of PTP domains indicated that two motifs, the KNRY motif and the WpD motif, are highly conserved in all PTP domains, but not in RPTP-D2s. In RPTPalpha-D2, the Tyr in the KNRY motif is substituted by Val (position 555) and the Asp in the WpD motif by Glu (position 690). Mutation of Val555 and Glu690 had synergistic effects on RPTPalpha-D2 activity, in that the PTP activity of RPTPalpha-D2-V555Y/E690D was greatly enhanced to levels that were similar to or approaching those of RPTPalpha-D1. Therefore, Val555 and Glu690 are responsible in large part for reduced RPTPalpha-D2 activity. In addition, we established that the increased PTP activity is due to restoration of effective transition-state stabilization in RPTPalpha-D2-V555Y/E690D. Since the KNRY motif and the WpD motif are mutated in all RPTP-D2s, it is highly unlikely, due to lack of transition-state stabilization, that the residual RPTP-D2 catalytic activity plays a role in the function of RPTPs.

Amino Acid Sequence↗
PubMed1998

Potentiation of G-protein-coupled receptor-induced MAP kinase activation by exogenous EGF receptors in SK-N-MC neuroepithelioma cells.

Lysophosphatidic acid (LPA) and endothelin-1 (ET-1), two ligands for G-protein coupled receptors (GPCRs), induce activation of mitogen activated protein kinase (MAPK). Surprisingly, LPA and ET-1 did not induce MAPK activation in SK-N-MC neuroepithelioma cells, even though these GPCR ligands evoked a rapid, transient rise in intracellular free Ca2+ concentration in these cells, indicating that SK-N-MC cells express functional LPA- and ET-1-receptors. Transient transfection of the EGFR into SK-N-MC cells, which do not express endogenous EGFR, potentiated LPA- and ET-1-induced MAPK activation. LPA and ET-1 did not enhance basal level tyrosine phosphorylation of the transfected EGFR in SK-N-MC cells. Even though the mechanism of LPA- and ET-1-induced MAPK activation in EGFR-transfected SK-N-MC cells remains to be determined definitively, our results provide strong evidence that the EGFR links these GPCRs to MAPK activation.

Animals↗
PubMed1997

Comparative kinetic analysis and substrate specificity of the tandem catalytic domains of the receptor-like protein-tyrosine phosphatase alpha.

The catalytic activity and substrate specificity of protein-tyrosine phosphatase alpha (PTPalpha) is primarily controlled by the membrane proximal catalytic domain (D1). The membrane distal (D2) domain of PTPalpha by itself is a genuine PTPase, possessing catalytic activity comparable to that of D1 using aryl phosphates as substrates. Surprisingly, kcat and kcat/Km for the D2-catalyzed hydrolysis of phosphotyrosine-containing peptides are several orders of magnitude reduced in comparison with those of D1. Substitution of the putative general acid/base Glu-690 in D2 by an Asp, which is invariably found in the WPD motifs in all cytoplasmic PTPases and all the D1 domains of receptor-like PTPases, only increases the kcat for D2 by 4-fold. Thus the much reduced D2 activity toward peptide substrates may be due to structural differences in the active sites other than the general acid/base. Alternatively, the D2 domain may have a functional active site with a highly stringent substrate specificity. PTPalpha display modest peptide substrate selectivity and are sensitive to charges adjacent to phosphotyrosine. In the sequence context of DADEpYLIPQQG (where pY stands for phosphotyrosine), the minimal sizes recognized by PTPalpha are either ADEpYLI or DADEpY-NH2.

Amino Acid Sequence↗
PubMed1997

Cell scattering of SK-N-MC neuroepithelioma cells in response to Ret and FGF receptor tyrosine kinase activation is correlated with sustained ERK2 activation.

The c-ret proto-oncogene encodes a receptor tyrosine kinase which plays an important role in kidney and enteric nervous system development. Germline mutations in c-ret are responsible for the dominantly inherited cancer syndromes, multiple endocrine neoplasia types 2A and 2B and familial medullary thyroid carcinoma as well as the developmental disorder Hirschsprung's disease. Using SK-N-MC neuroepithelioma cells stably transfected with an EGFR/Ret chimeric receptor, we have studied cellular consequences and signalling events following activation of exogenous EGFR/Ret and endogenous FGF and PDGF receptor tyrosine kinases in cells of neuroectodermal origin. Here we report that Ret activation led to cell scattering, growth inhibition and loss of anchorage-independent growth. Basic FGF, but not PDGF, evoked similar responses in those cells. Nevertheless, activation of all three receptor tyrosine kinases led to ERK2 activation. Analysis of the kinetics of ERK2 activation and downstream events revealed that Ret and FGF receptor activation led to sustained ERK2 activation and SRE transactivation, while PDGF treatment led to transient ERK2 activation and failed to induce SRE transactivation. Our results suggest that sustained, but not transient ERK2 activation may be involved in cell scattering.

Animals↗
PubMed1996

Structural basis for inhibition of receptor protein-tyrosine phosphatase-alpha by dimerization.

Receptor-like protein-tyrosine phosphatases (RPTPs), like their non-receptor counterparts, regulate the level of phosphotyrosine-containing proteins derived from the action of protein-tyrosine kinases. RPTPs are type-I integral membrane proteins which contain one or two catalytic domains in their cytoplasmic region. It is not known whether extracellular ligands regulate the activity of RPTPs. Here we describe the crystal structure of the membrane-proximal catalytic domain (D1) of a typical RPTP, murine RPTP alpha. Significant structural deviations from the PTP1B fold reside within the amino-terminal helix-turn-helix segment of RPTPalphaD1 (residues 214 to 242) and a distinctive two-stranded beta-sheet formed between residues 211-213 and 458-461. The turn of the N-terminal segment inserts into the active site of a dyad-related D1 monomer. On the basis of two independent crystal structures, sequence alignments, and the reported biological activity of EGF receptor/CD45 chimaeras, we propose that dimerization and active-site blockage is a physiologically important mechanism for downregulating the catalytic activity of RPTPalpha and other RPTPs.

Amino Acid Sequence↗
PubMed1996

Tight association of GRB2 with receptor protein-tyrosine phosphatase alpha is mediated by the SH2 and C-terminal SH3 domains.

Receptor protein-tyrosine phosphatase alpha (RPTPalpha), a transmembrane member of the extensive family of protein-tyrosine phosphatases (PTPs), is constitutively phosphorylated on Tyr789, a consensus binding site for the SH2 domain of the SH3-SH2-SH3 adaptor protein GRB2. We have previously shown that GRB2 binds to P.Tyr789 in vivo and in vitro via its SH2 domain. Here, we report that not only the GRB2 SH2 domain, but also the C-terminal SH3 domain is involved in binding to RPTPalpha in vitro and in vivo. Although the N-terminal SH3 domain of GRB2 is essential for binding to the Ras guanine nucleotide exchange factor Son of Sevenless (Sos), an RPTPalpha-GRB2-Sos complex could not be detected. The inclusion of peptides encompassing an hSos1 proline-rich motif in cell lysates resulted in enhanced binding of RPTPalpha to GRB2 in vitro, suggesting that steric hindrance prohibits formation of the RPTPalpha-GRB2-Sos complex. In vitro binding experiments indicated that the binding of GRB2 to Sos/dynamin and RPTPalpha was mutually exclusive. Analysis of in vitro binding kinetics coupled with results from transient co-transfections demonstrated that RPTPalpha is tightly bound to GRB2. The site of interaction of the C-terminal SH3 domain of GRB2 with RPTPalpha was mapped using deletion mutants to an 18-residue region in the N-terminal PTP domain. Arg469, within this region, was identified as one of the residues that is involved in the interaction with the C-terminal SH3 domain of GRB2. RPTPalpha residues 469-486 are localized close to the catalytic site cleft in the structure of the N-terminal PTP-domain, suggesting that interaction with the C-terminal SH3 domain may block access to the catalytic site, thus inhibiting RPTPalpha activity.

3T3 Cells↗
PubMed1996

Expression of receptor protein-tyrosine phosphatase alpha mRNA and protein during mouse embryogenesis.

Receptor protein-tyrosine phosphatase alpha (RPTP alpha) is a transmembrane member of the family of protein-tyrosine phosphatases (PTPs) that has been implicated in neuronal differentiation in vitro. Here we demonstrate that RPTP alpha is differentially expressed during mouse embryogenesis in a spatio-temporal manner. RPTP alpha expression was detectable in 6 days post coitum (dpc) embryos, but not in 7.5 dpc embryos. From 10.5 dpc onwards a striking RPTP alpha expression pattern was observed with elevated levels in the dorsal root ganglia, cranial ganglia and adrenal gland, suggesting that RPTP alpha levels are specifically enhanced in neural crest derivatives. Marked differences between RPTP alpha mRNA and protein levels indicated that RPTP alpha expression is regulated by transcriptional and (post-) translational mechanisms. The expression pattern of RPTP alpha suggests that RPTP alpha may play a role in neural crest cell differentiation in vivo.

Age Factors↗
PubMed1996

Activin and basic fibroblast growth factor regulate neurogenesis of murine embryonal carcinoma cells.

Murine P19 embryonal carcinoma (EC) cells can be differentiated into various germ layer derivatives. The addition of retinoic acid (RA) to P19-EC cell aggregates results in a transient activation of receptor protein tyrosine phosphatase-alpha (RPTP alpha). Subsequent replating of these aggregates leads to neuronal differentiation. P19-EC cells expressing constitutively active RPTP alpha (P19-RPTP alpha) show extensive neuronal differentiation upon RA treatment in monolayer. P19-RPTP alpha cells thus provide a suitable in vitro model for studying neuronal differentiation. We used P19-RPTP alpha cells to study the effects of activin and basic fibroblast growth factor (bFGF) on neurogenesis. We show that P19-RPTP alpha cells express mRNA for types I and II activin receptors. RA addition causes an up-regulation of receptor type IIA expression. Complexes of type I and II receptors were detectable by cross-linking assays both before and after RA treatment. Receptor complexes were functional as determined by transient transfection assays with activin responsive reporter constructs. Undifferentiated as well as differentiated P19-RPTP alpha cells express also the FGF receptors (FGFRs) FGFR-1 and FGFR-2 but not FGFR-3 and FGFR-4. Their functionality was established by bFGF induced mitogen-activated protein kinase phosphorylation. Activin and bFGF appeared to exert differential actions on RA-induced neuronal differentiation. Although activin irreversibly changes the differentiation fate into nonneuronal directions, bFGF does not affect initial neurogenesis but regulates axonal outgrowth in a concentration-dependent way; low concentrations of bFGF enhance axonal outgrowth, whereas high concentrations inhibit this process. These results strengthen the notion that activin and bFGF are important regulators of neurogenesis in the mammalian embryo.

Activin Receptors↗
PubMed1995

Why is phosphonodifluoromethyl phenylalanine a more potent inhibitory moiety than phosphonomethyl phenylalanine toward protein-tyrosine phosphatases?

The phosphonodifluoromethyl phenylalanine (F2Pmp) is superior to phosphonomethyl phenylalanine (Pmp) as a non-hydrolyzable phosphotyrosine (pTyr) mimetic. The difluoromethyl moiety increases the inhibitory potency of a F2Pmp-containing peptide over a Pmp-containing counterpart by 1000-fold toward the protein tyrosine phosphatase (PTPase), PTP1. Fluorine substitution at the methylene carbon have the double effect of lowering the phosphonate pKa2 as well as introducing hydrogen bonding interactions similar to the phosphate ester oxygen in pTyr. The inhibition of PTP1-catalyzed dephosphorylation reaction by both the F2Pmp and Pmp-containing peptides did not vary as a function of pH. The data indicate that both the monoanion and the dianion forms of the phosphonate bind PTP1 with equal efficiency. Thus, the better binding by the F2Pmp-peptide as compared to the Pmp-peptide is not due to the difference in pKa2. Taken together, these results offer an explanation for the increased affinity of F2Pmp for PTP1. The two fluorine atoms in F2Pmp may be able to interact with active site residues in PTP1 in a fashion analogous to that involving the phenolic oxygen and side chains in the active site of PTP1. Ki measurements for a simple phosphonic acid, Pmp- and F2Pmp-containing peptides suggest that although the principal recognition element is F2Pmp itself, the surrounding amino acids are required for high affinity binding. Comparative analysis of the inhibition of PTP1, PTP alpha and LAR by F2Pmp-containing peptides suggests that selective, tight-binding PTPase inhibitors can be developed.

Amino Acid Sequence↗
PubMed1995

Stimulation of receptor protein-tyrosine phosphatase alpha activity and phosphorylation by phorbol ester.

Receptor Protein-Tyrosine Phosphatase alpha (RPTP alpha) is a transmembrane protein with two cytoplasmic catalytic protein-tyrosine phosphatase (PTP) domains and a relatively short (123 amino acids) extracellular domain. Here we report that treatment of transfected cells that express RPTP alpha with the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate, a direct activator of protein kinase C, induced a rapid, transient increase in RPTP alpha activity due to a 2- to 3-fold increase in substrate affinity. A transient increase in RPTP alpha serine phosphorylation was concomitant with the enhanced activity. Tryptic phosphopeptide mapping of RPTP alpha demonstrated that phosphorylation of three tryptic peptides was enhanced in response to phorbol ester. In vitro dephosphorylation of RPTP alpha from phorbol ester-treated cells reduced RPTP alpha activity to prestimulation levels, indicating that enhanced serine phosphorylation directly accounted for the increase in activity. Our results demonstrate that serine phosphorylation may play a key role in the regulation of the activity of transmembrane PTPs.

Cell Line↗
PubMed1994

Phosphorylation of receptor protein-tyrosine phosphatase alpha on Tyr789, a binding site for the SH3-SH2-SH3 adaptor protein GRB-2 in vivo.

Receptor protein-tyrosine phosphatase alpha (RPTP alpha) is a transmembrane protein with a short extracellular domain (123 amino acids) and two cytoplasmically localized protein-tyrosine phosphatase (PTP) domains. Here we report that RPTP alpha is constitutively phosphorylated on tyrosine in NIH 3T3 mouse fibroblasts. The in vivo tyrosine phosphorylation site was localized to the C-terminus of RPTP alpha by phosphopeptide mapping experiments using in vivo and in vitro 32P-labeled RPTP alpha. The identity of this site as Tyr789, located five residues from the C-terminus, was confirmed by site-directed mutagenesis. Transient overexpression of c-Src together with RPTP alpha in human embryonic kidney 293 cells increased phosphorylation of Tyr789, suggesting that c-Src may phosphorylate RPTP alpha in vivo. RPTP alpha had autodephosphorylation activity in vitro. When expressed in 293 cells the level of Tyr789 phosphorylation was higher in a non-functional mutant of RPTP alpha than in wild type RPTP alpha, indicating that RPTP alpha may have autodephosphorylation activity in vivo as well. The sequence on the C-terminal side of Tyr789 (YANF) fits the consensus binding site for the SH3-SH2-SH3 adaptor protein GRB2 (YXNX). We show that RPTP alpha, but not a mutant of RPTP alpha with a Tyr-->Phe mutation at position 789, bound to GRB2 in vitro. In addition, RPTP alpha co-immunoprecipitated with GRB2 from NIH 3T3 cells, demonstrating that GRB2 bound to RPTP alpha in vivo. The guanine nucleotide releasing factor for the Ras GTPase, Son of sevenless (Sos), which associates with GRB2 via its SH3 domains, was not detected in RPTP alpha immunoprecipitates. Our results suggest a role for RPTP alpha in attenuation of GRB2-mediated signaling.

3T3 Cells↗
PubMed1993

Receptor protein tyrosine phosphatase alpha activates pp60c-src and is involved in neuronal differentiation.

Here we report that protein tyrosine phosphatases (PTPases), like their enzymatic counterpart the protein tyrosine kinases, can play an important role in cell differentiation. Expression of the transmembrane PTPase receptor protein tyrosine phosphatase alpha (RPTP alpha) is transiently enhanced during neuronal differentiation of embryonal carcinoma (EC) and neuroblastoma cells. Retinoic acid induces wild type P19 cells to differentiate into endoderm- and mesoderm-like cells. By contrast, retinoic acid treatment leads to neuronal differentiation of P19 cells, ectopically expressing functional RPTP alpha, as illustrated by their ability to generate action potentials. Endogenous pp60c-src kinase activity is enhanced in the RPTP alpha-transfected cells, which may be due to direct dephosphorylation of the regulatory Tyr residue at position 527 in pp60c-src by RPTP alpha. Our results demonstrate that RPTP alpha is involved in neuronal differentiation and imply a role for pp60c-src in the differentiation process.

Animals↗
PubMed1993

Multiple and cooperative phosphorylation events regulate the CREM activator function.

Phosphorylation is one of the major mechanisms by which the activity of transcription factors can be regulated. We have investigated the role of phosphorylation in the regulation of the transcription factor CREM. We show that the CREM tau activator is phosphorylated on multiple serine and threonine residues in vivo. Stimulation of various signal transduction pathways by forskolin, TPA or Ca2+ ionophore leads to enhanced phosphorylation of serine 117, concomitant with an increase in the transactivation potential of CREM tau. We have identified multiple kinases that can also phosphorylate S117 in vitro. Moreover, we show that casein kinase I and II cooperatively phosphorylate CREM tau on multiple residues, eliciting enhanced DNA binding. Cooperative phosphorylation is also observed with other kinases. These results show that the activity of CREM tau is regulated by multiple phosphorylation events, suggesting that CREM could be considered as a nuclear effector where signalling pathways may converge and/or cross-talk.

3T3 Cells↗
PubMed1992

Differential expression of a novel murine non-receptor protein tyrosine phosphatase during differentiation of P19 embryonal carcinoma cells.

Protein phosphorylation on tyrosine residues is one of the major mechanisms of cell signal transduction and is regulated by protein tyrosine kinases and protein tyrosine phosphatases. Here we report the molecular cloning of an additional member of the protein tyrosine phosphatase-family from differentiated murine P19 embryonal carcinoma cells. This non-receptor protein tyrosine phosphatase, P19-PTP, does not contain regulatory sequences, homologous to the ones found in other non-receptor PTPases. P19-PTP is differentially expressed during in vitro differentiation of P19 EC cells, in that P19-PTP mRNA could only be detected in embryoid bodies, derived from P19 cells.

Amino Acid Sequence↗
PubMed1992

Epidermal growth factor activates calcium channels by phospholipase A2/5-lipoxygenase-mediated leukotriene C4 production.

Epidermal growth factor (EGF) induces a Ca2+ influx in many cell types, but the underlying mechanisms are so far unresolved. We report that: EGF-induced Ca2+ channel activity is eliminated by lipoxygenase inhibition and is mimicked by artificial induction of lipoxygenase activity; addition of leukotriene C4 can fully mimic EGF in its ability to activate Ca2+ channels; and EGF induces a rapid accumulation of intracellular leukotriene C4. In addition, we show that EGF-induced, Ca(2+)-dependent membrane hyperpolarization and junB proto-oncogene expression are dependent on lipoxygenase activity, whereas EGF-induced cytoplasmic alkalinization is not. We conclude that PLA2/5-lipoxygenase-mediated leukotriene C4 production constitutes a novel and specific signal transduction pathway in growth factor action.

Acetophenones↗
PubMed1992

EGF-induced jun B-expression in transfected P19 embryonal carcinoma cells expressing EGF-receptors is dependent on Jun D.

The TPA-inducible transcription factor AP-1, consisting of homo- or hetero-dimers of members of the Jun- and Fos-families, regulates transcription of a wide variety of genes containing the TPA response element (TRE). In P19 embryonal carcinoma (EC) cells, Jun D is the only component of AP-1 expressed, while in these cells until now none of the members of the jun- and fos-families have been found to be inducable by external stimuli. Here we demonstrate that Jun B is the only member of the Jun- and Fos-families that is induced by Epidermal Growth Factor (EGF) in transfected murine P19 EC cells, expressing functional human EGF receptors (hEGF-Rs). Induction of jun B can be mimicked in wild type P19 EC cells by the synergistic action of the phorbol ester TPA and the calcium ionophore A23187, through activation of signal transduction pathways, that are activated simultaneously by EGF. The EGF induced jun B expression in the hEGF-R expressing P19 EC cells is mediated by an inverted repeat (IR) sequence in the jun B promoter, previously shown to be responsive to both PKC and PKA signal transduction. Transactivation of the IR sequence by EGF can be blocked completely by prior expression of antisense Jun D, but not by antisense c-Jun. These studies therefore implicate Jun D in the regulation of immediate early gene expression by external stimuli.

Blotting, Northern↗
PubMed1991

Characterization of a tyrosine kinase signaling pathway in undifferentiated P19 embryonal carcinoma cells.

Embryonal carcinoma (EC) cells are the malignant stem cells of teratocarcinoma and have the capacity to proliferate in the absence of serum growth factors. As yet no receptor protein tyrosine kinases have been identified on undifferentiated EC cells and as a consequence tyrosine kinase signaling pathways could not be studied in these cells. We have used stably transfected P19 embryonal carcinoma cells expressing a well-characterized receptor protein tyrosine kinase, the human epidermal growth factor receptor (hEGF-R) to study protein tyrosine kinase signaling mechanisms in undifferentiated EC cells. Here we report that the ectopically expressed hEGF-R contains EGF-inducible autophosphorylation activity and is rapidly internalized and degraded upon ligand binding. In addition, the exogenous hEGF-R confers EGF-responsiveness to these cells in that inositol phosphate formation and cytoplasmic-free Ca2+ concentration are enhanced in response to EGF. Furthermore, the Na+/H+ exchanger is activated in response to EGF, leading to a sustained rise in intracellular pH. Our results show that undifferentiated P19 EC cells contain the necessary components of protein tyrosine kinase signal transduction machinery.

Adenosine Triphosphate↗